Patent Document 1 discloses an oil pump for the art applicable to a fuel pump that draws fuel into pump chambers and then discharges fuel in succession. This pump includes an outer gear having inner teeth, an inner gear that includes outer teeth and is eccentric relative to the outer gear in an eccentric direction to be engaged with the outer gear, and a pump housing that accommodates the outer gear and the inner gear to be rotatable in the circumferential direction. The outer gear and the inner gear rotate to draw oil into the pump chambers and then discharge oil in succession, with the volume of the pump chambers formed between both these gears increased or decreased.
This pump housing includes a sliding surface on which the outer gear and the inner gear slide, and a suction guide passage that suctions oil into the pump chamber and a discharge guide passage that discharges oil from the pump chamber as guide passages that are recessed from this sliding surface to extend in the circumferential direction. A suction side end part of the suction guide passage and a discharge side end part of the discharge guide passage are opposed to each other with a gap therebetween.
The pump chamber between the suction side end part and the discharge side end part forms a chamber which is a gap having a closed shape.